Autumn Mule Deer Foods on Heavily Grazed Cattle Ranges in Northwestern Colorado

Abstract

The botanical composition of the diets of domestic cattle and mule deer (Odocoileus hemionus) was estimated by microscopically examining fecal samples collected on deer winter ranges heavily used by cattle. Diet overlap ranged from 1 to 22% (‘x = 12%) on the nine areas studied. When cattle are forced from a grass dominated diet to browse forage on overgrazed ranges, diet overlap and therefore forage competition increases between deer and cattle. The effects of excessive livestock use on the winter range of mule deer continues to be controversial in the Rocky Mountain Region, especially since less than 50% as many deer are harvested now as were 20 years ago. Recent literature suggests that diet overlap of domestic cattle and mule deer in northwestern Colorao was about 4% in 1975 (Hubbard and Hansen 1976; Hansen and Clark 1977; Hansen et al. 1977). Many wildlife biologists believe dietary overlap between mule deer and cattle should be much higher and some literature published 20 to 40 years ago supports this contention (Robinson 1931, 1973; Interstate Deer Herd Committee 1947). An objective of this study was to select mule deer wintering sites which appeared to have been continuously abused by livestock for many years, and to determine early winter foods selected by mule deer and cattle on these same sites. We hypothesized that in these extreme cases, diet overlap would be higher than on ranges in better condition.